1. Field of the Disclosure
The invention relates to a medical or dental handpiece which has a multi-stage transmission arrangement with at least two planetary gear transmissions connected one after the other, in particular a dental surgical handpiece for emplacing and removing implants.
2. Related Technology
In the case of medical and in particular dental treatment instruments there is often desired a rapid movement, in particular a high speed of rotation of the treatment tool. Dental drills, for example, achieve in use as a rule 30,000 revolutions per minute and more. These high rotary speeds are attained by means of an appropriate configuration of the electric or pneumatic motors. Alongside this, however, there are also kinds of treatments with which significantly lesser rotary speeds are desired for the treatment tool. If, for example, dental implants are to be placed in the jaw or removed, although high torques up to 30 Ncm are needed, however, only rotary speeds in the range of 4000 to 5000 revolutions per minute are needed.
In order to be able to employ the electric or pneumatic motors normally provided at dental work stations also for these kinds of treatment, there are put to use handpieces which have a transmission arrangement for stepping down the drive speed of rotation at the motor. These so-called step-down transmissions can be realized in various manners, however, preferably so-called planetary transmissions are employed, which make possible a particularly good transfer of the power flux. A dental handpiece having a planetary transmission is for example known from DE 42 21 403 C2.
The stepping down of the speed of rotation via a single planetary transmission is, while retaining optimal force transfer, possible only up to a certain degree. In order to obtain a step down of the speed of rotation going beyond this, it is known from U.S. Pat. No. 5,569,034 to form a multi-stage transmission arrangement of a plurality of planetary transmissions connected one after the other. With this known arrangement, the planetary gear carrier of one transmission stage forms the drive shaft for the next following transmission stage, so that a many-fold reduction of speed of rotation is made possible, depending upon the number of transmission stages connected one after the other. FR 2 530 454 A1 also describes a dental handpiece having two planetary transmissions connected one after another.
With the arrangement of U.S. Pat. No. 5,569,034 the individual transmission stages are in each case formed by identical components, whereby at the output end of one component the planetary gear carrier projects and carries on its outside the sun gear for the next following transmission stage. Upon putting together of the overall transmission arrangement, one transmission stage is then placed on the other, whereby the projecting planetary gear carrier of one stage engages in each case into the rearward end of the next stage.